The present invention relates to a display apparatus for displaying a two- or three-dimensional image using display means such as a CRT, a liquid crystal panel, or the like and, more particularly, to a display apparatus suitable for a head-mount display apparatus, and its control method.
As a system which changes its display contents in correspondence with the movement of a user""s head, a head-mount display apparatus is known. In a system of this type, it is a general practice to move the display region of the head-mount display apparatus, as indicated by bold frames in FIG. 9. Note that a portion surrounded by a broken line in FIG. 9 corresponds to a wide image region prepared in advance on a memory. As indicated by arrows in FIG. 9, a portion surrounded by the bold frame is moved in correspondence with the movement of the head, and the range of the bold frame is extracted and displayed on the entire display screen of the head-mount display apparatus.
As another method, a method of detecting the movement of an observer""s head, calculating an image to be displayed in correspondence with the detected movement of the head, and generating and displaying an image by a CG (COMPUTER GRAPHICS) technique on the basis of the calculation result is known.
As described above, in a case where the head-mount display changes its display contents in correspondence with the movement of a user""s head, an image range must be large enough to cover the movement of the head. Therefor, required capacity of an image memory is large. Furthermore, since the head-mount display extracts the display contents to be displayed from the image memory and changes its extracting portion in correspondence with the movement of the head, high access speed is required. Therefore, to display a natural and real image corresponding to the head movement by using the conventional head-mount display, the system scale has to be large and complex.
In the case of the CG system which generates an image corresponding to the head movement by a calculation, an image cannot be displayed in real time due to a heavy calculation load, resulting in unnatural images which are intermittently displayed frame by frame. In this case, since a special-purpose processor and circuit are required, the cost increases, and the apparatus scale increases.
In recent years, large-screen, three-dimensional video systems have become popular. In contrast to this, an apparatus for observing an image is required to attain size and weight reductions. As a display apparatus which satisfies such requirements, spectacle- and helmet-type head-mount display apparatuses have been developed.
Each of these apparatuses comprises compact two-dimensional image display units such as CRTs, liquid crystal displays, or the like corresponding to the right and left eyes, and a user wears such an apparatus on his or her head or face to project images displayed on these image display units onto the retinas of the right and left eyes via an optical system. Therefore, such a display apparatus is superior to a stand-alone type display in terms of its space factor and portability.
Also, the above-mentioned display apparatus can also realize a three-dimensional image display since it comprises two display units for the right and left eyes.
However, in the conventional apparatus, the field angle of an image to be displayed is determined by the dimensions of the display units such as CRTs, liquid crystal displays, or the like to be used in the apparatus, and the magnification of the optical system. In order to obtain sufficient reality, a large field angle is generally preferable, but it does not always apply. Each image to be observed has an optimal field angle, and if the field angle of the apparatus is considerably different from the optimal field angle, an observer often feels fatigue. More specifically, upon observation of an image with rapid movement on an excessively large screen, since the movement itself of an image becomes large, the observer must move his or her eyes or face largely, resulting in an increase in fatigue.
Furthermore, in order to solve such a problem, an optical system which can vary its magnification may be used to change the field angle. However, with this arrangement, the optical system itself becomes large in size, and the apparatus scale increases accordingly. For this reason, superiority such as compactness, light weight, and the like, of the head-mount display apparatus to the stand-alone type display is lost.
The present invention has been made in consideration of the above-mentioned problems, and has as its object to provide a display apparatus and its control method, which can attain a natural display in real time in correspondence with the movement of a head even under the condition of a limited memory capacity.
It is another object of the present invention to provide a display apparatus and its control method, which can prevent the display state from oversensitively responding to an unnecessary movement of the head of an observer, and can reduce the fatigue of the observer.
It is still another object of the present invention to provide a display apparatus and its control method, which can limit the change direction of the display state in correspondence with the purpose of use and display contents of a head-mount display apparatus, and the observer""s favor to effectively obtain reality, and to reduce the fatigue of the observer.
It is still another object of the present invention to provide a display apparatus and its control method, which can automatically control the limitation on the change direction of the display state on the basis of video data supplied to a head-mount display apparatus, and allow an observer to easily enjoy video effects that a video creator intended.
It is still another object of the present invention to provide a display apparatus and its control method, which can change the field angle of an image to be displayed without increasing the size of an optical system in display units which are respectively disposed at the observation positions of the right and left eyes.
It is still another object of the present invention to provide a display apparatus and its control method, which can automatically realize a display at an optimal field angle in correspondence with each image input to the display apparatus.
It is still another object of the present invention to provide a display apparatus and its control method, which allow an observer to easily synthesize right and left images by changing the positions of images to be displayed on right and left display units.
It is still another object of the present invention to provide a display apparatus and its control method, which allow an observer to observe an image under an optimal condition associated with the field and convergence angles by automatically displaying an image at an optimal position in correspondence with each image input to the display apparatus.